Paul L. Brown

Evaluation of the free ion activity model of metal-organism interaction: extension of the conceptual model

The present study integrates the concepts of the free ion activity model (FIAM) into biological receptor theory (BRT; i.e. pharmacodynamic principles) to obtain a more rigorous conceptual model; one that more precisely quantifies the interaction of chemical species at biological receptor sites. The developed model, which is viewed as an extended FIAM, explains the conditions under which the FIAM will be effective in explaining biological response (BR). It establishes that BR is directly proportional to the activity of the free metal ion in the linear regions of concentration-response curves only. Additionally, it indicates that [X-cell], the activity of free surface sites on the cell membrane, does not need to be constant in the region of BR, as assumed by the original FIAM. The extended FIAM was tested by re-examining concentration-response data from the literature on aquatic organisms exposed to several ecotoxicologically-relevant trace metals. These data, which would be considered exceptions to the original FIAM, were found to be consistent with the extended FIAM. Due to its more rigorous conceptual basis, the extended FIAM is capable of modelling concentration-response experiments from a wider range of water chemistry conditions (i.e. varying pH, hardness and dissolved organic matter) than the original model and, as such, potentially provides a more useful tool for evaluating metal-organism interactions. This study proposes, for the first time, a quantitative method of uncoupling the biological effects of a metal hydroxide (1:1) complex from that of amelioration of the free metal ion (M(z+)) by H(+). Since the activities of H(+) and metal-hydroxide cannot be independently varied, it has been previously very difficult to evaluate whether metal-hydroxide species contribute to eliciting a BR. Furthermore, the extended FIAM can directly derive fundamental information from concentration-response curves, such as the binding constants of H(+) or the hardness cations (Ca(2+) and/or Mg(2+)) to the cell membrane surface of aquatic organisms.

Chemical speciation of environmentally significant metals with inorganic ligands Part 2: The Cu2+-OH-, Cl-, CO32-, SO42-, and PO43- systems (IUPAC Technical Report)

The numerical modeling of CdII speciation amongst the environmental inorganic ligands Cl–, OH–, CO32–, SO42–, and PO43– requires reliable values for the relevant stability (formation) constants. This paper compiles and provides a critical review of these constants and related thermodynamic data. It recommends values of log10βp,q,r° valid at Im = 0 mol kg–1 and 25 °C (298.15 K), along with the equations and empirical reaction ion interaction coefficients, ∆ε , required to calculate log10βp,q,r values at higher ionic strengths using the Brønsted–Guggenheim–Scatchard specific ion interaction theory (SIT). Values for the corresponding reaction enthalpies, ∆rH, are reported where available. Unfortunately, with the exception of the CdII-chlorido system and (at low ionic strengths) the CdII-sulfato system, the equilibrium reactions for the title systems are relatively poorly characterized. In weakly acidic fresh water systems (–log10 {[H+]/c°} < 6), in the absence of organic ligands (e.g., humic substances), CdII speciation is dominated by Cd2+(aq), with CdSO4(aq) as a minor species. In this respect, CdII is similar to CuII [2007PBa] and PbII [2009PBa]. However, in weakly alkaline fresh water solutions, 7.5 < –log10 {[H+]/c°} < 8.6, the speciation of CdII is still dominated by Cd2+(aq), whereas for CuII [2007PBa] and PbII [2009PBa] the carbonato- species MCO3(aq) dominates. In weakly acidic saline systems (–log10 {[H+]/cϒ} < 6; –log10 {[Cl–]/c°} < 2.0) the speciation is dominated by CdCln(2–n)+ complexes, (n = 1–3), with Cd2+(aq) as a minor species. This is qualitatively similar to the situation for CuII and PbII. However, in weakly alkaline saline solutions, including seawater, the chlorido- complexes still dominate the speciation of CdII because of the relatively low stability of CdCO3(aq). In contrast, the speciation of CuII [2007PBa] and PbII [2009PBa] in seawater is dominated by the respective species MCO3(aq). There is scope for additional high-quality measurements in the Cd2+ + H+ + CO32– system as the large uncertainties in the stability constants for the Cd2+-carbonato complexes significantly affect the speciation calculations.

Population biology of carp (Cyprinus carpio L.) in the mid-Murray River and Barmah Forest Wetlands, Australia

The present study quantitatively describes a significant stock of carp (Cyprinus carpio L.), an exotic pest species, in a temperate riverine floodplain wetland. Intensity and duration of flooding influenced relative abundance, distribution and recruitment. Average growth (mm) in length was described with the von Bertalanffy growth model for males (L∞ = 489, k = 0.249, t0 = –0.519), and females (L∞ = 594, k = 0.177, t0 = –0.609) to age 28. Variation in growth was described with a lognormal distribution of k. Total mortality (Z year–1) was 0.268–0.407 for males, 0.311–0.422 for females, 3.24 for age-0 juveniles and 1.80 for age-1 juveniles. Natural mortality (M year–1) was 0.199 for males and 0.262 for females. Fishing mortality (F year–1) was <0.05 for males and 0.11–0.30 for females. Gonadal changes indicated extended spawning seasons peaking in September 1999 and October 2000. Median sizes and ages at initial maturation were 307 mm, 584 g and 1.1 years for males and 328 mm, 688 g and 2.7 years for females. Sex ratio varied significantly with age from equal as juveniles to a significant male-bias as adults. This description will enable better stock assessment and development of simulations that evaluate potential pest management strategies.

Divalent metal accumulation in freshwater bivalves: an inverse relationship with metal phosphate solubility.

Whole soft tissue concentrations of Mn, Co, Ni, Cu, Zn, Pb, Cd and U were measured in two species of freshwater (unionid) bivalves (Hyridella depressa and Velesunio ambiguus) from a minimally polluted site in the Hawkesbury-Nepean River, south-eastern Australia. Although the mean concentrations of metals in the tissue were similar for each bivalve species, their patterns of accumulation were dissimilar. For each metal, positive linear relationships between tissue concentration and shell length (r2 = 0.37-0.77; P < or = 0.001) and tissue dry weight (r2 = 0.29-0.51; P < or = 0.01) were found in H. depressa, but not in V. ambiguus. However, for both species, positive linear relationships were found between the tissue concentration of each divalent metal and Ca tissue concentration (r2 = 0.59-0.97; P < or = 0.001). For both bivalve species, the normalised rates of accumulation of the metals relative to increasing Ca concentration and/or size, were U approximately = Cd > or = Pb > or = Mn > Co > or = Zn > Cu > Ni. The differential rates of accumulation of divalent metals are interpreted as being predominantly governed by their varying loss rates, which are controlled by the differing solubilities (log Ksp values) of the metals in the phosphatic extracellular granules, the demonstrated major sites of metal deposition in the tissue of H. depressa and V. ambiguus. The rates of accumulation of Mn, Co, Zn, Cu and Ni were linearly and inversely related (r2 = 0.91-0.97; P < or = 0.001) to their solubilities as hydrogen phosphates, a finding consistent with the bioaccumulation model previously developed for the alkaline-earth metals. However, for U, Cd and Pb, this linear inverse relationship did not continue to hold, i.e. their rates of accumulation did not increase with decreasing solubility. However, these results are still consistent with the model if U, Cd and Pb are so insoluble in the granules of H. depressa and V. ambiguus over their lifetime (up to approx. 50 years) that there is effectively no loss of these metals, and hence, no differential between their rates of accumulation. The present results reaffirm the use of Ca tissue concentration to predict the tissue concentrations of other divalent metals by explaining up to 94 and 97% of the variability between individual bivalves of H. depressa and V. ambiguus, respectively. The use of Ca tissue concentration to effectively minimise the inherent variability between individuals in their metal tissue improves the ability of an investigator to discern smaller spatial and/or temporal differences in the metal tissue concentrations of these bivalves, and thus to detect metal pollution.

Dissolved organic carbon reduces uranium bioavailability and toxicity. 1. Characterization of an aquatic fulvic acid and its complexation with uranium[VI].

Fulvic acid (FA) from a tropical Australian billabong (lagoon) was isolated with XAD-8 resin and characterized using size exclusion chromatography, solid state cross-polarization magic angle spinning, 13C nuclear magnetic resonance spectroscopy, elemental analysis, and potentiometric acid-base titration. Physicochemical characteristics of the billabong FA were comparable with those of the Suwannee River Fulvic Acid (SRFA) standard. The greater negative charge density of the billabong FA suggested it contained protons that were more weakly bound than those of SRFA, with the potential for billabong water to complex less metal contaminants, such as uranium (U). This may subsequently influence the toxicity of metal contaminants to resident freshwater organisms. The complexation of U with dissolved organic carbon (DOC) (10 mg L(-1)) in billabong water was calculated using the HARPHRQ geochemical speciation model and also measured using flow field-flow fractionation combined with inductively coupled plasma mass-spectroscopy. Agreement between both methods was very good (within 4% as U-DOC). The results suggest that in billabong water at pH 6.0, containing an average DOC of 10 mg L(-1) and a U concentration of 90 μg L(-1), around 10% of U is complexed with DOC.

Uranium and other contaminant migration in groundwater at a tropical Australian Uranium Mine

Hydrogeochemical modelling (utilising the modelling tools MODFLOW, MT3D and HARPHRQ) has been used in conjunction with laboratory-based experiments and a field monitoring program to investigate the fate of uranium and other contaminants in excess water sprayed on a 33 ha region of the Ranger Uranium Mine (RUM), northern Australia. The results indicate that uranium is retained in the surficial layer of the lateritic soils of the area. Conservative contaminants are not retained by the soils and are transported into the groundwater. Subsequently, they migrate relative to the groundwater flow rate towards the river system down hydraulic gradient of the irrigation area.

The hydrolysis of uranium(VI)

Summary The hydrolysis of uranium(VI) has been investigated in 0.10 mol dm−3 NaClO4 and KCl and 1.0 mol dm−3 KNO3 using the potentiometric technique. The results of the data analysis have been combined with data previously obtained from this laboratory and the literature to provide a more definitive description of the hydrolysis behaviour of uranium(VI). The species UO2OH+, (UO2)2(OH)22+, (UO2)3(OH)42+, (UO2)3(OH)5+ and (UO2)4(OH)7+ have been identified in nitrate media and all but the last of these species in chloride and perchlorate media. The differences in the complexation behaviour in the media may be due to oxoanion binding by the nitrate, a process which has also been observed for sulfate.

Hydrogeochemical characteristics and importance of natural and anthropogenic influences on soil and groundwater in reclaimed land adjacent to Port Jackson, Sydney, Australia

Major ion and trace metal concentrations and physicochemical parameters were measured over a full tidal cycle in groundwater from reclaimed land adjacent to Rozelle Bay in Port Jackson, Sydney, Australia. Materials used for reclaiming the land (construction material waste or dredged marine sediment) predominantly influenced the ion and trace element compositions of the groundwater. The redox behaviour and composition of the soil profiles influenced the behaviour of redox-sensitive elements in the groundwater, for example Mn and Fe. When the water table recedes in drier periods, oxygen ingress can lead to biologically catalysed oxidation reactions resulting in a reduction in pH and an associated increase in the concentration of some trace elements. The dredged marine sediment contains a considerable fraction of shell fragments, leading to elevated bicarbonate levels in the groundwater, which in turn limits some trace element and major ion concentrations. The groundwaters contain higher levels of many trace elements (Cu, Pb, Zn, As, Cr) than occur in seawater and the natural hydraulic gradient may lead to elevated concentrations of these elements entering the estuary.

The use of kinetic modelling as a tool in the assessment of contaminant release during rehabilitation of a uranium mine

Abstract Geochemical kinetic modelling codes have been utilised in the assessment of the potential for contaminant release during the rehabilitation of mine sites. Two uranium mines in eastern Germany have been used as study sites for the application of the kinetic models. Results from the study will be used in the formulation of options for the rehabilitation of the two sites. The predicted results are in good agreement with results from other studies using different techniques and can also predict the water quality of pilot-scale flooding experiments.

Kinetics of 45Ca, 60Co, 210Pb, 54Mn and 109Cd in the tissue of the freshwater bivalve Velesunio angasi : further development of a predictive and mechanistic model of metal bioaccumulation

A theoretical and experimental study was performed to determine the kinetics of 45Ca, 60Co, 210Pb, 54Mn and 109Cd in the whole soft tissue of the unionid bivalve Velesunio angasi. This investigation further tested the hypothesis, developed previously for the alkaline-earth metals, that the biological half-life of a metal in soft tissue is related to its solubility when deposited in the extracellular granules of the bivalve. This hypothesis was tested for the above radionuclides (tracers of the stable metals) by a comparison of (a) a qualitative a priori prediction of their biological half-lives in bivalve tissue, based on critically evaluated log Ksp values for their respective hydrogen phosphate salts, and calibrated to previous experimentally determined rates of loss for 45Ca and 226Ra, with (b) their empirical biological half-lives that were investigated experimentally using the radionuclides 45Ca, 60Co, 210Pb, 54Mn and 109Cd. The results of the experimental investigation showed that the mean values calculated for the biological half-lives of 45Ca and 60Co in the tissue were 106 and 121 days, respectively, but there was no significant (P > 0.05) loss of 210Pb, 54Mn or 109Cd from the soft tissue over 160 days, when bivalves were exposed to radionuclide-free water. A chemical model was developed from first principles that quantitatively explains the kinetic mechanisms that underlie the differential rates of loss of divalent metals from the extracellular granules of V. angasi. The experimental results were consistent with the predictions of the model; however, some investigational limitations were evident, and these are discussed. The uptake of each radionuclide into the bivalve tissue tended to be linear, but the variation in tissue concentration, between individual bivalves, increased with the period of exposure. Significant (P < 0.001) positive correlations were found between tissue concentrations of each radionuclide pairing in both the uptake and loss phases of the experiment, indicating that individual bivalves were internally consistent in the way that they metabolised these radionuclides.